High-quality capacitors are an integral part of many electrical circuits. Capacitors are available in a variety of values with different characteristics. Variable capacitors having a wide dynamic range are available only in bulk sizes rendering them useless for miniature electronic applications. Semiconductor variable capacitors, referred to as varactors, are available, however with very narrow dynamic range. Tunable electronic circuits such as filters and oscillators are presently tuned using fixed components for coarse tune and tunable capacitors or inductors for fine tune.
Electronic devices, and in particular communication devices, utilize a variety of circuits such as filters and oscillators that must be tuned for proper operation. These circuits use a combination of fixed and tunable components to achieve their objectives. Fixed components are used along with tunable components to provide the tunable circuit with sufficient dynamic range. The need for fixed value components has resulted in the inability to design and manufacture a common circuit to operate over a desired range. Communication devices operating in a particular band must be proliferated to perform at different segments of that band due to the unavailability of alternative and tunable components. Each board is equipped with a different fixed value component along with a variable characteristic component to achieve the desired performance specifications.
Another area of deficiency in electronic devices is the area of distributed resistive-capacitive networks. These networks are particularly beneficial in communication devices. Present distributed networks are also used in proliferation. That is, several circuits are designed and fabricated which perform the same function at different regions of their performance spectrum. The impact of proliferation is obvious on product cost, inventory, handling, troubleshooting, quality and a score of other problems. Some techniques have been employed to avoid proliferation with some degree of success. One such technique is laser trimming of printed components. This procedure only available to high frequency applications is limited in range and can only reduce the number of boards performing similar functions and not totally eliminating the need for such proliferation. A need is therefore clear for a tunable network having a wide dynamic range with reactive characteristics.